1. Field of the Invention
The present invention relates to a touch-panel device, and more particularly, to a technology of detecting a touched position in a projected capacitive type touch-panel device.
2. Description of the Related Art
A touch-panel device (also called touch screen) is a user interface device which includes an input device called touch pad and an output device formed of, for example, a flat panel display, in which the input device and the output device are integrally formed. The touch-panel device has a feature of an intuitive operation method in which an operation target displayed on a display is directly touched with a finger or the like, and is widely used for an information terminal device or the like.
There are various methods of implementing the touch-panel device, and one of those methods includes a projected capacitive type system. According to the projected capacitive type system, a plurality of electrodes are arranged on the touch panel, and a touched position is detected based on a change in electrostatic capacitance of the electrodes caused when a fingertip approaches the touch panel. The electrodes are formed of a material with high transmittance and arranged on the display panel, to thereby form a touch-panel device.
Accuracy of touched position detection may be referred to as a performance index of a touch panel as an input device. When an error between a position on the display panel actually touched by a user and a detected position is smaller, the accuracy is higher.
JP 2003-511799 A (hereinafter, referred to as Patent Document 1) discloses a method as an example of a technology of detecting a touched position with high accuracy in a projected capacitive type touch-panel device. According to the touched position detecting method, electrodes for detecting positions in an X direction and a Y direction are arranged in a pattern so as to allow a fingertip to touch a plurality of electrodes simultaneously when touching the display panel, to thereby determine the touched position with high accuracy.
Alternatively, JP 2008-269297 A (hereinafter, referred to as Patent Document 2) employs an electrode pattern in which electrodes for detecting positions in an X direction and a Y direction are formed on a single layer, to thereby reduce the manufacturing process.